1. Field of the Invention
The present invention relates to a fusion welding method for binding the surfaces of two metals, and particularly to a fusion welding method by applying a powdery medium on the metal binding surfaces so as to form eutectics at same surfaces upon sintering the surfaces in vacuum, thereby fusing and welding the binding surfaces of the two metals together.
2. Description of Prior Art
Conventionally, "welding" process carried out at a higher temperature has normally been adopted for binding two metals so as to obtain a higher binding strength as compared with the case of "soldering" process carried out at a temperature below 450.degree. C. by employing lower melting point solder such as tin or lead. Instead of lower melting point solder used in "soldering", brazing solder of higher melting point, mainly composed of noble metals containing gold, silver, copper, nickel, etc, is usually used in "welding" process. Brazing solder composed of the above noble metals mixed by certain ratio will form eutectics, thus lowering the melting point of the brazing solder, which is normally in the range of about 600.degree. C. to 1100.degree. C. that may be selected depending on welding condition.
For instance, in the fabrication of the head portion of the golf club, the bottom of the head portion needs to be bound with a weight of a higher specific gravity so as to lower the center of gravity of the head portion. As a result, an initial swing of the club can hit the ball to a further distance. In addition, the hitting plate of the head portion should be made of composite materials formed through special metal processing or heat treatment so as to obtain high strength and high coefficient of elasticity. Thus, the hitting plate may withstand impact and may produce a light sound upon hitting the ball. FIG. 1 shows a schematic view illustrating the binding of a weight to the head portion of the golf club by a conventional welding method. First, provide a recess 111 in the bottom surface 11 of the head portion. Then, coat a layer of brazing solder 12 on the bottom surface of the recess 111, and press a weight 13 to fit into the recess 111 over the layer of brazing solder 12. Subsequently, the entire structure is placed into a vacuum furnace for sintering at a temperature slightly higher than the eutectic point of the brazing solder 12. Through such a sintering process in vacuum, the brazing solder 12 melts first, and then, under high temperature, the melt brazing solder 12 penetrates into the bottom surface 11 and the weight 13 due to capillary penetration, so as to bind the bottom surface 11 and the weight 13 together.
Though the above conventional welding method is superior to soldering method in its obtainable binding strength, it suffers from the below drawbacks:
1. Expensive brazing solder composed of noble metals; PA0 2. Relatively higher binding cost; PA0 3. Necessity of pressing the two metals to be bound against each other; PA0 4. Restriction to the thickness of the coated brazing solder; PA0 5. Necessity of relatively precise control in welding process for obtaining better binding effect; and PA0 6. Poor welding effect if the metal to be bound has a density larger than 14 g/cm.sup.3 because, in this case, capillary penetration becomes poor. PA0 1. The cost of fabrication is high because titanium screw is expensive and a polishing step must be employed. PA0 2. In the state wherein the weight 13 is screw fastened to the bottom surface 11, a gap is always remained between the weight 13 and the recess 111. This gap differs from one golf club to another due to the fabrication precision of the weight 13 and the recess 111, or due to difference in the applied force for tightening the screws 14. The unevenness in the gap between the weight 13 and the recess 111 of the bottom surface 11 will cause difference in the sound produced when the head portion of the golf club hits a ball, thus resulting in unevenness in the quality of the golf club. Consequently, its is difficult to control the quality of the produced golf club by use of this conventional method.
FIG. 2 shows another conventional way of attaching a weight to the head portion of the golf club. A weight 13 is screw fastened to the bottom surface 11 of the head portion by a plurality of (only one is shown in FIG. 2) screws 14 made of titanium for improving the rust protection effect and obtaining higher fastening strength at the fastened portion. Each screw 14 penetrates through a through hole 131 provided in the weight 13 and then threaded into a screw hole 112 provided in the bottom surface 11 corresponding to a through hole 131. After that, the heads of the screws 14 are polished to provide an overall aesthetic appearance.
This conventional method of screw fastening two metals has the drawbacks as follows: